Topic: FTTH PON Types

FTTH
PON: Passive Optical Network
A PON system utilizes a passive splitter that takes one
input and splits it to "broadcast" signals downstream to
many users. This reduces the cost of the system
substantially by sharing one set of electronics and an
expensive laser with up to 32 homes. Upstream, the passive
splitter acts as a combiner to connect all users to the
same shared PON port. An inexpensive laser is used for the
home to send signals back to the FTTH system in the
central office.

Triple
Play Systems
Most FTTH systems are so-called "triple play"
systems offering voice (telephone), video (TV) and data
(Internet access.) To provide all three services over one
fiber, signals are sent bidirectionally over a single
fiber using several wavelengths of light.BPON, or
broadband PON, was the most popular PON application in the
beginning. BPON uses ATM as the protocol. ATM is widely
used for telephone networks and the methods of
transporting all data types (voice, Internet, video, etc.)
are well known. BPON digital signals operate at ATM rates
of 155, 622 and 1244 Mb/s.

Downstream digital signals from the CO through the
splitter to the home are sent at 1490 nm. This signal
carries both voice and data to the home. Video on the
first systems used the same technology as CATV, an analog
modulated signal, broadcast separately using a 1550 nm
laser which may require a fiber amplifier to provide
enough signal strength to overcome the loss of the optical
splitter. Video could be upgraded to digital using IPTV,
negating the need for the separate wavelength for video.
Upstream digital signals for voice and data are sent back
to the CO from the home using an inexpensive 1310 nm
laser. WDM couplers separate the signals at both the home
and the CO.

BPON
architecture with analog TV

GPON, or
gigabit-capable PON, uses an IP-based protocol and either
ATM or GEM (GPON encapsulation method) encoding. Data
rates of up to 2.5 Gb/s are specified and it is very
flexible in what types of traffic it carries. GPON enables
“triple play” (voice-data-video) and is the basis of most
planned FTTP applications in the near future. In the
diagram above, one merely drops the AM Video at the CO and
carries digital video over the downstream digital link.

EPON or
Ethernet PON is based on the IEEE standard for Ethernet in
the First Mile. It uses packet-based transmission at 1
Gb/s with 10 Gb/s under discussion. EPON is widely
deployed in Asia. The system architecture is the same as
GPON but data protocols are differenet.

PON
System Specification Summary

BPON

GPON

EPON

Standard

ITU-T
G.983

ITU-T
G.984

IEEE
802.3ah (1 Gb/s)
IEEE 802.3av (10Gb/s)

Downstream
Bitrate

155,
622 Mb/s, 1.2 Gb/s

155,
622 Mb/s, 1.2, 2.5 Gb/s

1.25
Gb/s, 10.3 Gb/s

Upstream
Bitrate

155,
622 Mb/s

155,
622 Mb/s, 1.2, 2.5 Gb/s

1.25
Gb/s, 1.25 or 10.3 Gb/s

Downstream
Wavelength

1490,
1550

1490

1490,
1550

Upstream
Wavelength

1310

1310

1310

Protocol

ATM

Ethernet
over ATM/IP or TDM

Ethernet

Video

RF
at 1550 or IP at 1490

RF
at 1550 or IP at 1490

IP
Video

Max
PON Splits

32

64

16

Transmitter
Power*

OLT:
~0 to +6 dBm, ONT: ~ -4 to +2 dBm

Power
Budget*

~13dB
(min) to 28dB (max) w/32 split

~13dB
(min) to 28dB (max) w/32 split

Coverage

<20
km

<60
km

<20
km

* There are several versions of each type that vary so
these are typical ranges.

RFOG:
CATV's FTTHCATV
operators were the first broadband providers using a HFC
(hybrid fiber coax) system with cable modems using RF
signals. Today, some CATV operators see a need for a
system to provide fiber to the home, which has lead to the
development of RFOG (RF over Glass.) CATV standards have
looked at PON architectures and the SCTE has proposed a
standard for deploying a broadcast architecture of analog
signals similar to PONs called RFoG for RF (radio
frequency - i.e. FM) over Glass. RFOG is basically nothing
more than an all-fiber HFC/cable modem system built with
less expensive components now available thanks to the
volume pricing of components used in FTTH. It’s designed
to operate over a standard telco PON (passive optical
network) fiber architecture with short fiber lengths and
including the losses of a FTTH PON splitter.

There
is one interesting aspect of this approach. Now telcos and
CATV companies can deliver the same services over the same
cable plant using totally different technologies. But that
means that office or apartment building owners, developers
or even whole towns that might be considering installing
FTTH infrastructure themselves and leasing the fiber to a
service provider can have a choice of service providers.
One cable network can support either CATV or telco systems
– or even someone else for that matter. That opens up a
big market for private fiber optic systems.

WDM
and PONObviously,
PON networks use WDM (wavelength-division multiplexing)
with different wavelengths upstream and downstream. But
the PON architecture can easily support more wavelengths,
allowing greater bandwidth to the user but allocating one
wavelength to a user or a group of users or greater
security by having each user have their own wavelength.
WDM PON architectures are being developed by many
companies but no standards exist for them yet.

Other
Uses For PONsPONs
offer low cost connectivity for a large number of users
with high security and relatively low management needs.
Some PON suppliers have been promoting PONs as an
alternative to LANs (Local Area Networks), which are
especially attractive to organizations with large numbers
of users. Passive
Optical LANs are claimed to be less expensive than
traditional copper cabling for LANs but offer virtually
unlimited future expansion. See
Premises/Networks
for more information on POLs.